The present invention relates generally to aircraft fuselage, and more particularly to a reinforced aircraft skin and a method for reinforcing aircraft skin.
Most commercial and military aircraft have finite operational lives that span several decades. As a result, many airlines and the military operate aircraft that are decades old. Among the various problems which are common to aging aircraft, material fatigue is one of the most critical. Component failure that is caused by fatigue or flaws in the materials of some components can have a catastrophic effect on aircraft.
Most aircraft cabins are pressurized during high altitude flight to provide comfort for the passengers. The pressure difference between the inside and the outside of an aircraft increases and decreases as the aircraft climbs and descends, respectively, to higher and lower altitudes during flight. In essence, the aircraft body structure or fuselage acts as a pressure vessel by maintaining a constant pressure that is close to one atmosphere inside the aircraft body.
The cyclical deflections of the fuselage caused by cyclical pressurization and depressurization of the aircraft can create small cracks in a skin of the fuselage that propagate with additional cyclical expansion and contraction of the aircraft body. At some point during flight, a large crack may propagate so fast that the section of skin on which the crack occurs exposes the inside of the aircraft body to the outside environment, thus causing rapid depressurization of the cabin. The skin can also become instantly dislodged from the aircraft body when catastrophic failure occurs, in which case, sudden depressurization can cause some passengers and objects to be sucked out of the cabin. Furthermore, aerodynamics of the aircraft can be so severely affected as a result of a large skin panel becoming dislodged from the aircraft body that maintaining flight or controlling the aircraft during flight may become impossible.
The skin fatigue or catastrophic failure problems can be improved or solved by strengthening aircraft skin to reduce flexure during in-flight pressurization cycles. Increasing the skin thickness is one possible solution, but an impractical one at best. A thicker skin layer adds weight to the aircraft, which in turn reduces the payload capacity, the flight range, and/or the aerodynamic efficiency of the air craft. This in turn translates into fewer passengers and/or a reduction in cargo capacity, resulting in increased operating costs. A more practical solution should increase the strength of the skin layer without adding significant weight to the aircraft. A practical solution should also be cost effective, not create other unforeseeable hazards to passengers and crew, be easily adaptable to existing and new aircraft, be insoluble in materials that are used in aircraft operation, and not hinder the performance and cost effectiveness of aircraft.
U.S. Pat. No. 5,251,849 suggests one such solution. The patent discloses affixing a polymer foam material to the interior side of an aircraft skin material to reduce structural failures caused by metal fatigue resulting from many cycles of in-flight pressurization and depressurization.
In accordance with an aspect of the teachings of the present invention, an aircraft fuselage or body structure has a skeleton frame and a skin layer affixed to at least part of the skeleton frame. The aircraft body structure is strengthened by affixing a composite reinforcing layer to at least a substantial portion of an interior surface of the skin layer. The composite reinforcing layer includes a polymer foam material combined with a reinforcing material.
In accordance with another aspect of the teachings of the present invention, a method is disclosed for strengthening an aircraft body structure having a skeleton frame and an aircraft skin layer affixed to at least a portion of the skeleton frame. The method includes adding a reinforcing material to a polymer foam material to form a composite reinforcing layer. The method also includes affixing the composite reinforcing layer to at least an interior surface of the skin layer.